Cable Television (CATV) networks have been undergoing rapid upgrading, particularly in North America, in order to provide advanced services, such as digital video, telephony and Internet services. A major part of the upgrade cycle has been the development of the return path network—the path from residential subscribers to the CATV Headend. Previously, this portion of the network was used little, generally only for minor maintenance and billing operations. As interactivity needs grew and CATV technology advanced, this portion of the network became more significant. Now, the return path forms a critical portion of the system for two-way interactivity, such as telephony and data traffic.
The current field implementation of digitized return path solutions for HFC fiber nodes employs a direct digitization and transmission of the entire return path signal spectrum. Some instances of this implementation can provide a means for digitizing two of these signals, and transmitting both using Time Division Multiplexing of the digital signals. Each of these digitized return path signals can typically generate a digital signal rate anywhere in the range of 800 Mbps to 2.25 Gbps depending on the signal band, sampling rate and the number of bits used to sample each signal. When combining two or more of these signals, the aggregate digital signal rate can increase beyond the capabilities of existing low-cost digital and optical transport platforms. This situation perpetuates as technologies evolve, because enhanced services become possible that are enabled with such technology improvements. Furthermore, decreasing the bit rate of optical transport would represent cost saving opportunities.
The present invention is therefore directed to the problem of developing a method and apparatus for transmitting multiple return path signals, from a multi-port optical note for example, using lower data rate components and lasers than would normally be possible to send the information.